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Polyurethane Adhesives for Composite Packaging: Current Status and Development Trends
The composite flexible packaging material is a composite material in which two or more different types of substrates (films) have different properties and are tightly adhered by an adhesive. At present, China's most used and best performing adhesives in composite flexible packaging materials are solvent-based two-component polyurethane adhesives. This type of adhesive has a history of 50 to 60 years in foreign countries. However, in China, there are only 25 years of application history. It was imported from abroad to manufacture composite flexible packaging materials in the early 1980s. In 1981, Shanghai's research results passed national-level technical appraisal, and in 1984 it achieved industrial production. After more than 20 years of development, there are currently hundreds of companies in China producing this product, with an annual production capacity of about 100,000 tons. The actual output last year was about 3,560 tons. The products offered are both general and functional; both resistant to low temperatures and resistant to temperatures up to 135°C; used for food and pharmaceutical packaging, but also resistant to liquid pesticides; both aromatic, There are also aliphatic; both solvent-based and solvent-free; both ester-soluble and alcohol-soluble. In general, other countries have, we have.
The following is a detailed analysis of the history, status quo and development trend of polyurethane adhesive for composite packaging in China.
Development status
The development of composite flexible packaging materials in China started later than abroad. In the second half of the 70s of the last century, Shanghai began researching composite materials for food packaging using extrusion compounding and dry compounding. In 1982, Shanghai, Dalian, and Wuxi took the lead in introducing advanced large-scale flexible packaging production equipment from Japan, forming a complete set of intaglio printing machines, dry laminating machines, extrusion laminators, slitters, bag making machines, and testing equipment. The production system also began to use imported aluminum foil, polyester film, polypropylene, inks and adhesives.
At the end of 1984, China used the technology approved by the state in 1981 to build the first factory to produce solvent-based two-component polyurethane adhesive for food packaging, which made people see the prospect of localization of adhesives. In the short period of two to three years, more than ten adhesive production enterprises have rapidly developed and the scale is relatively large. The annual output is 200 to 500 tons.
In the early 90s of the last century, China's packaging industry made rapid progress, and imported flexible packaging lines emerged everywhere. Enticing the huge market, adhesive production plants are also rapidly developing. According to recent statistics, about 300 companies across the country have produced dry compound adhesives with an annual production capacity of about 100,000 tons. Two-component polyurethane adhesives have been localized for more than 20 years. Not only are there a lot of manufacturers, product models have also been enriched, and the quality of certain brands has reached the international level. In recent years, domestic products have accounted for more than 85% of the total domestic consumption.
In order to occupy the Chinese market, many foreign companies have invested in factories in China. Japan's Takeda Pharmaceuticals Co., Ltd. has already started production at its production facility in Suzhou and provides ordinary low-cost adhesives to the Chinese market. Rohm and Haas Company of the United States has also set up a factory in Shanghai. After the acquisition of Morton, in addition to promoting water-based adhesives, it also sells solvent-based adhesives. Henkel's factory in Shanghai has put into production of UK2860 polyurethane compound adhesive.
Among domestic adhesives, research and development and product quality in Shanghai and Beijing have always been ahead of others. From a historical point of view, from the development of common adhesives to hot and acid resistant media resistant adhesives, from room temperature adhesives to boiling resistant to high temperature cooking adhesives, from general adhesives to functional Adhesives, from solvent-based adhesives to solvent-free adhesives, from aromatic adhesives to aliphatic polyurethane adhesives, to anti-corrosive adhesives adapted to certain liquid EC pesticide packaging, from non- From flame-retardant adhesives to fully-flame-retardant adhesives, Shanghai's scientific and technological personnel have played an important role in pioneering and the quality of products is also at the forefront. Products manufactured using Shanghai technology can not only replace imports but also receive foreign materials. With the approval of users, the export of domestic polyurethane adhesives was realized in the early 1990s.
Now, Shanghai, Beijing, Zhejiang, Jiangsu, and Guangdong can provide polyurethane adhesives for composite food packaging materials with various properties and meet various packaging requirements. Among them, Shanghai Lianyin Chemical Co., Ltd. can produce high temperature resistance and resistance at the same time. LY-50A/LY-50AH adhesive with dielectric erosion and LY-103A/LY-103B functional aluminized composite adhesive, and LY-9850R that can be used for aluminum foil structure and 121-135°C high temperature cooking /LY- 9875R, LY-135A/LY-135B adhesives and LY-9850F/LY-9875F aliphatic urethane adhesives that are compliant with FDA regulations and resistant to 121～124°C high temperature cooking, and LY-50VR And LY-50VN Liquid Emulsion Pesticide Packaging Adhesive, and in 2001 it successfully developed LY-75FT/LY-75FTH Adhesive with fast curing and no increase in the coefficient of friction of the composite film, shortening the curing time and reducing The two factors of friction coefficient and good openness are not inferior to those of similar imported products. Beijing Research Institute of Chemical Industry has UK2850/UK5000 plastic/plastic compound resistant to 121°C, 30 minute cooking adhesive and UK8150/UK7330 solvent free adhesive. Guangdong Zhongshan Kanghe Company has a special aluminum adhesive film adhesive KH-VM80. The European and American companies in Shenzhen have ECO501A/B and ECO751A/B alcohol-soluble adhesives, and Beijing Gaomeng Chemical has YH502 high-temperature cooking adhesives.
development trend
The development trend of adhesives for composite flexible packaging has the following six directions.
1. Towards high solids, low viscosity adhesives
The earliest two-component polyurethane adhesive whose solid content of the main agent is 35% or 50% has now been increased to 75% or 80%, and the European region has increased to 88%, which is almost no solvent! The solid content of the curing agent also increased from the original 60%, 75% to about 80%. This is mainly to reduce the amount of solvent emissions and reduce production costs.
In the past, due to the relationship between the equipment and the process, the adhesive was required to have excellent initial tack to ensure that the composite did not produce wrinkles or "tunneling" defects at the time under the equipment and process conditions, so the molecular weight of the adhesive Very high viscosity, and the concentration of the operating solution during compounding is low, (mostly 20% to 30%), to ensure that the pre-set amount of glue and uniform coating effect, as well as the composite product quality. Obviously, this low-concentration coating will inevitably lead to a large amount of solvent volatilization into the atmosphere, for example, the concentration of the operating solution is 20%, the amount of glue is 3.5g/m2, then, the coating is applied on a per square meter basis. The weight of the adhesive on the film is 3.5/0.20=17.5 (g). When dry, 14 g of solvent per square meter becomes air discharged into the air, leaving only 3.5 g of dry-based adhesive. This situation will lead to two big problems.
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